Method and apparatus for controlling the concentration of vapors in the atmosphere



Patented Mar. 22, 1949 OFFICE UNITED STATES Oswald Hope Robertson, Theodore T. Puck, and Henry l/lJise, Ohicago, lll., assignors to the United States of America as represented by the Secretary of War Application October 3l., 1945, Serial No. 625,824

4 Claims.

This invention relates to a method and apparatus for controlling the concentration o vapors in the atmosphere and more particularly to detection, measurement and control of condensible vapors; such as are used for killing air-borne bacteria and viruses, although not limited thereto.

It has been found that certain chemical agents, and particularly propylene and triethylene glycols may be very effectively employed to kill aerial bacteria and viruses in rooms occupied by human beings. However, considerable dimculty is encountered in maintaining a vapor concentration between that which is necessary to accomplish bactericidal action and the saturation level. This margin is relatively narrow; and while excessive concentration of the more commonplace compounds used for aerial disinfection, and especially propylene or triethylene glycols, is in no way harmful to the health of the occupants of the room, the tugging of the atmosphere is undesirable.

It is among the objects of the present invention to more eiciently control the concentration of vapors in the atmosphere, and particularly such vapors as are used for killing air-borne bacteria and viruses.

The invention, then, comprises the features hereinafter fully described, and as particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail a certain illustrative embodiment of the invention, this being indicative of but one of several Ways in which the principles of the invention may be successfully employed.

In the drawings:

Figure 1 is a side elevation, partly in section, of the apparatus of the invention; and

Figure 2 is a diagrammatic showing of an electrical circuit which may be employed to operate the apparatus of Figure 1.

Referring more particularly to the drawings, the numeral 2 designates a base upon which there is disposed a rectangular housing 3. The bottom of the housing 3 provides a tank l containing Water, the surface level of which is maintained at a constant level by any suitable means (not shown). Mounted on the base 2, and exteriorly of the housing 3 is a slow-speed electric motor 5 which drives a gear-reduction unit 6. The driven shaft I of the gear reduction unit extends into the housing 3 and carries a metallic disk 9, the latter having a highly polished periphery. In contact with each side of the metallic disk 9 there is a smaller disk l of cloth or other absorbent material. These absorbent disks, or wicks It, are

attached to the metallic disk 9' in any suitable manner, as by means of clamping disks l2 and/ or stitched threads extending through apertures in the disk 9 which may be provided for this purpose. In any case, the metallic disk 9 and the smaller absorbent disks I0, form a unit which, through the agency of the slow-speed electric motor 5 and the gear-reduction unit t, is rotated at very slow speed, such, for example, as one-tenth or one-rifteenth of a revolution per minute.

As shown, the lower ends of the rotating metallic disk s, and its associated absorbent disks i0, depend into the constant-level water supply in the tank Al. Thus, the absorbent disks lil take on water by capillary attraction; and the effect of the evaporation of the absorbed water is to eiectively cool the metallic disk 9. A series of narrow radial slots i3 in the metallic disk 9, and in the absorbent disks l0, serve to diminish heat conduction from the lower p-art of this assembly.

As the rotating highly polished periphery of the metallic disk 9 emerges from the water in the tank ll, it is wiped clean by a rubber scraper yIl which presses against the same. In this manner there is continuously presented a fresh surface on which condensation may take place.

Immediately above the tank Il, and in radial alignment with the highly polished periphery of the metallic disk 9, the housing 3 is provided with an air inlet i8 which communicates with the at.- mosphere. Opposite the air inlet I8, the housing 3 is provided with an air outlet 20, immediately adjacent which there is disposed a suction fan 2 l the latter being driven by an adjacently disposed electric motor 22.

According to the foregoing construction and arrangement, it will be perceived that vapor in the atmosphere of a room may be drawn into the housing t and permitted to impinge and condense upon the highly polished periphery of the metallic disk 0 after which it will sweep across the faces of the absorbent disks I0. The rapid evaporation of the water from the moistened surfaces cools the metallic disk 9 to a temperature which is approximately that of wet-bulb temperature.

This type of cooling eliminates the possibility of the condensation of water vapor from the air on the highly polished periphery of the metallic disk 9. If water vapor condensation should occur the method of the invention would become useless for the detection of any other vapor. However, such an occurrence is prevented by cooling the metallic disk 9 in the manner described. At wet-bulb temperature the condensation of water vapor alone (dew point) is not possible regardless of what relative humidity obtains. Any other result of changes in the relative humidity on the effectiveness of the method of the invention for triethylene glycol will be small because two factors which operate in opposite directions are brought into play. An increase in relative humidity increases the degree of saturation of the vapor in the air and hence its tendency to condense. However, the temperature of the metallic disk 9 simultaneously rises because of the rise in the wet-bulb temperature, so that the extent of condensation tends to diminish. Thus. these two factors tend to compensate for each other.

We have found that the extent of the condensation on the highly polished periphery of the metallic disk 9 depends directly on the concentration of the condensable vapor in the ambient air. The condensation on the periphery of the metallic disk takes the form of a ne film; and the teachings of the present invention contemplate ineasuring the optical characteristics thereof. and more specifically the degree to which the condensate interferes with the reflection of a beam or light into a light sensitive instrument. Thus, the reduction in the intensity of the reflected light beam depends directly upon the extent of this condensation which, in turn, depends upon the initial concentration of the condensable vapor in the air.

As shown in the drawings, there is mounted atop the housing 3 a light box 25 within which there is disposed a suitable electric light bulb 26, such, for example, as a 6-volt automobile headlight bulb. The light rays emitted from this light bulb 26 are directed through an aperture 28 in the housing 3 and onto the highly polished periphery of the metallic disk 9. The light rays so directed are reflected from the periphery of the disk 9 onto an adjacent mirror Sil and from the said mirror back onto the periphery of the disk. By the use of this mirror 3E), the beam of light is made to undergo two reflections from the periphery of the disk 9, so that the effect of the light reduction due to the lm of the condensate is increased, and an increased sensitivity is thus obtained. After the light rays have been projected from the mirror 3D back onto the periphery of the metallic disk 9 they are reflected through an aperture 32 in the housing 3 onto a photoelectric cell 34 which is disposed in an adjacent case 35. Suitable lenses are provided for the light bulb 26 and the photoelectric cell 34, as shown at 26a, and 34a, respectively.

By interference and scattering, the film of condensate on the highly polished periphery of the metallic disk 9 diminishes the intensity of the light reected onto the photoelectric cell 34. Thus, when condensible vapor is present in the air the output of the photoelec'tric cell is reduced.

As shown in the electrical circuit of Figure 2, the photoelectric cell Sil is connected to a single stage electronic amplifier, and is made to operate a relay which in turn controls the degree of energization or output of the vaporizer. As previously stated, the vapor utilized may acceptably take the form of propylene or triethylene glycol. Step-down transformers are included in the circuit for energizing the light bulb 26 and the photoelectric cell 34.

The amplifier Voltage may be adjusted so that any desired glycol concentration can be maintained in the air. When this concentration is reached, the thickness of the film on the periphery of the cool wheel is just sumcient to reduce the light reflected into the photocell to the point where the'relay disconnects the glycol vaporizer. Then, as the concentration of glycol vapor in the air gradually diminishes, the extent of condensation also decreases and the amount of light entering the photocell begins to increase, ultimately reaching an intensity at which the glycol vaporizer is again turned on. A rise in temperature increases the capacity of the air to contain glycol vapor and, hence, less glycol condenses on the cooled periphery of the metallic disk 9. This is presumably the very same process which is responsible for the decreased bactericidal efciency of a given concentration of glycol vapor with increase in temperature, i. e., a diminished extent of condensation on the bacterial droplet. Thus, the principle of the mechanism by which the glycostat regulates the vapor concentration is precisely the same as that which controls the bactericidal action.

A voltmeter connected across the output of the amplifier tube, as shown in Figure 2, records quantitatively the degree of light extinction due to the film of condensed vapor. Once the instrument is calibrated these readings can be converted directly into degree of saturation of the air by glycol vapor.

By the use of the apparatus of the invention we have been able to determine concentrations of glycol vapors in air of the order of a few thousandths of a milligram per liter of air, or less. By causing the relay to control the operation of the glycol vaporizer it is possible to maintain the concentration of the vapor in the air at any desired level.

Having thus described our invention, what we claim as new and wish to secure by Letters Patent l. Apparatus for quantitatively determining the presence of vapors in an atmosphere which condense at temperatures above the dew point comprising a light-reflecting surface, means for passing a sample of said atmosphere in Contact with said surface, means for maintaining said surface at approximately the wet-bulb temperature of said atmosphere, a. light source for directing light rays onto said surface, and light-sensitive means for measuring the opacity of the condensate.

2. Apparatus for controlling vaporizers comprising a light-reflecting surface, means for passing a sample of vapor bearing atmosphere in contact with said surface, said vapors being c-ondensible above the dew point temperature of said atmosphere, means for maintaining said surface at approximately the wet-bulb temperature of said atmosphere, a light source for directing light rays onto said surface, and light-sensitive means for varying the vapor output -of said vaporizer in accordance with the opacity of the condensate.

3. The method of quantitatively determining the presence of vapors in a vapor-bearing atmosphere, said vapors being condensible above the dew point temperature of said atmosphere, which comprises passing the said atmosphere over a condensing surface for the vapors, maintaining the surface at approximately the wet-bulb temperature of said atmosphere to effect condensation of vapors thereon, and measuring the opacity of the condensate.

4. The method of controlling vaporizers, which comprises passing a vapor-bearing atmosphere over a condensing surface for the vapors, said vapors being condensible above the dew point temperature of said atmosphere, maintaining the surface at approximately the wet-bulb temperature of said atmosphere to effect condensation of vapors thereon, measuring the opacity of the resulting condensate, and varying the vapor output of the vaporizer in accordance with the said opacity.

OSWALD HOPE ROBERTSON. THEODORE T. PUCK. HENRY WISE.

REFERENCES CITED The following references are of record in the le of this patent:

5 UNITED STATES PATENTS Number Name Date 1,651,236 Thwing Nov. 29, 1927 1,860,377 Anderson May 31, 1932 1o 1,960,658 Brace May 29, 1,934 

